The Death Star was an important project for the Empire, with Geonosians designing the technological foundation and achieving the highest level of technology. For many years, many people lavishly invested large sums of money to achieve the emperor's goals. In order to overcome the limitations of technology at the time, Director Krennic adds Galen Erso to the project (Project Stardust).
Although the Geonosians had built a strong and stable foundation, their technology for managing energy sources (cores) and the theory of systems for supplying energy to their weapons were incomplete.
Although we were able to successfully solve the problem with Galen Erso, it was a system that inevitably had other technical problems. It may be more accurate to think of it as a technical compromise. Krennic was so focused on completing the Death Star that he was unaware of the vulnerability of the compromise.
With more time, he could have minimized the technical compromises, but he was forced to overlook them in order to meet the Empire's construction schedule.
In other words, the real flaws in the Stardust program are not technical, but rather artificial on the part of those who carried it out. The Empire pushed forward with an aggressive schedule, resulting in a series of technological compromises on the Death Star itself. A typical example is a heat-dissipating ventilation duct.
In fact, Galen Erso took advantage of this situation and intentionally implanted a technical flaw in the Death Star. He pretended to be worried about Krennic and secretly discovered a way to destroy the Death Star.
The more Krennic is unable to meet the Empire's schedule, the more stressed he becomes, so Galen Erso is conveniently placed to fill in the flaws. So he deliberately dragged it out to meet the construction schedule.
Remember, the Stardust project is top secret.
In order to maintain secrecy, it must be constructed using the minimum resources of the empire. Not only the technical aspects, but also the people who carry out the work and the process of overseeing the situation are inevitably weakened. Therefore, they could not be wary of Gairen Aso.
The construction of the later Second Death Star did not have to be classified, so it went very smoothly.
In addition to his previous lessons, he entrusted Lord Vader with the process of overseeing the personnel and circumstances in which it was carried out.
It will also be possible to attract rebel forces during construction, in other words, incorporate military operations into the construction schedule.